Variable valve system of internal combustion engine and method of assembling same

ABSTRACT

A variable valve system of an internal combustion engine varies an operation manner of an engine valve by controlling an angular position of a control shaft. The system comprises a stopper mechanism that determines an angular range in which the control shaft is permitted to rotate about its axis; an actuating mechanism that actuates the control shaft to rotate about its axis; and a position matching device that is practically assembly only when the actuating mechanism is being assembled. The position matching device, when assembled, restricts operation of the actuating mechanism in such a manner as to match a maximally operated position of the actuating mechanism with a maximally operated angular position of the control shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a variable valve system ofan internal combustion engine, which is able to vary a lift degree (orwork angle) of engine valves (viz., intake and/or exhaust valves) inaccordance with an operation condition of the engine. More specifically,the present invention relates to such variable valve system and a methodof assembling the same.

2. Description of the Related Art

Hitherto, in the field of variable valve systems of an internalcombustion engine, various types have been proposed and put intopractical use. One of the systems is shown in U.S. Pat. No. 6,615,777.

The variable valve system of this US patent generally comprises a valvelift varying mechanism that, by rotating a control shaft, varies a liftdegree (or work angle) of engine valves (viz., intake and/or exhaustvalves) and an actuating mechanism that drives or rotates the controlshaft in accordance with an operation condition of the engine.

The actuating mechanism comprises an electric motor, an output shaftdriven by the electric motor, a screw nut having an inner thread meshedwith an outer thread formed on the output shaft, a link member having aforked end pivotally connected to diametrically opposed portions of thescrew nut through bearing pins and a lever member having one endpivotally connected to the other end of the link member and the otherend rotatably connected to the control shaft through a pin. The controlshaft has adjusting cams integrally connected thereto.

When, upon energization of the electric motor, the output shaft isrotated about its axis, the screw nut is moved axially forward orrearward along the output shaft pivotally moving both the link memberand the lever member. With this, the control shaft is turned about itsaxis to a desired angular position.

SUMMARY OF THE INVENTION

However, due to its inherent construction, the actuating mechanismdisclosed by the above-mentioned US patent fails to show an exactposition control of the screw nut relative to the output shaft. Morespecifically, because of the nature of the meshed engagement between thescrew nut and the output shaft, the maximally moved position of thescrew nut relative to the output shaft is not exactly defined orcontrolled, which tends to induce a poor positioning of the controlshaft at the maximally turned angular position. Of course, such poorpositioning of the control shaft has an undesired influence on thecontrollability of the variable valve system.

It is therefore an object of the present invention to provide a variablevalve system of an internal combustion engine, which is free of theabove-mentioned drawback.

That is, an object of the present invention is provide a variable valvesystem of an internal combustion engine, which can exhibit a satisfiedcontrollability of the system throughout all ranges of the angularposition of the control shaft.

In accordance with a first aspect of the present invention, there isprovided a variable valve system of an internal combustion engine forvarying an operation manner of an engine valve by controlling an angularposition of a control shaft, which comprises a stopper mechanism thatdetermines an angular range in which the control shaft is permitted torotate about its axis; an actuating mechanism that actuates the controlshaft to rotate about its axis; and a position matching device that ispractically assembled only when the actuating mechanism is beingassembled, the position matching device when assembled restrictingoperation of the actuating mechanism in such a manner as to match amaximally operated position of the actuating mechanism with a maximallyoperated angular position of the control shaft.

In accordance with a second aspect of the present invention, there isprovided a variable valve system of an internal combustion engine forvarying an operation manner of an engine valve by controlling an angularposition of a control shaft. The variable valve system comprises astopper mechanism that determines an angular range in which the controlshaft is permitted to rotate about its axis; and an actuating mechanismthat actuates the control shaft to rotate about its axis, the actuatingmechanism comprising an externally threaded shaft that is turned aboutits axis in accordance with the operation condition of the engine; aninternally threaded nut member operatively engaged with the threadedshaft so that turning of the threaded shaft induces an axial movement ofthe nut member along the threaded shaft, the nut member beingcontactable with the position matching device when the latter isassembled; a transmission mechanism provided between the control shaftand the nut member to convert the axial movement of the nut member to arotary motion of the control shaft; a housing that houses therein thethreaded shaft, the threaded nut member and the transmission mechanism;and a position matching device that is practically assembled only whenthe actuating mechanism is being assembled, the position matching devicewhen assembled restricting operation of the actuating mechanism in sucha manner as to match a maximally operated position of the actuatingmechanism with a maximally operated angular position of the controlshaft.

In accordance with a third aspect of the present invention, there isprovided a method of assembling a variable valve system of an internalcombustion engine, the variable valve system varying an operation mannerof an engine valve by controlling an angular position of a control shaftand comprising a stopper mechanism that determines an angular range inwhich the control shaft is permitted to rotate and an actuatingmechanism that actuates the control shaft to rotate about its axis. Themethod comprises placing a positioning bolt at a given position of a wayalong which an element of the actuating mechanism moves, the givenposition being a position where the element contacts the positioningbolt when the stopper mechanism causes the control shaft to take amaximally operated position; causing the element of the actuatingmechanism to contact with the positioning bolt; connecting the actuatingmechanism and the control shaft; removing the positioning bolt from thegiven position; placing a close bolt to the given position in place ofthe positioning bolt.

Other objects and advantages of the present invention will becomeapparent from the following description when taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectional plan view of a variable valve system ofthe present invention;

FIG. 2 is a front view of a stopper mechanism employed in the variablevalve system of the present invention;

FIG. 3 is a sectional view of an essential portion of the variable valvesystem of the invention, showing a connection between a control shaftand an actuating mechanism;

FIG. 4 is a sectional view of the actuating mechanism in a condition toinduce the minimum lift of engine valves;

FIG. 5 is a view similar to FIG. 4, but showing a condition to inducethe maximum lift of intake valves of the engine;

FIG. 6 is a sectional view of a portion of the variable valve systemwhere a positioning bolt is operatively engaged with a positioningopening;

FIG. 7 is a view similar to FIG. 6, but showing a condition wherein aclose bolt is engaged with the positioning opening in place of thepositioning bolt;

FIG. 8 is a perspective view of the variable valve system of the presentinvention;

FIGS. 9A and 9B are views taken from the direction of the arrow “A” ofFIG. 8, in which FIG. 9A shows a valve closing operation under thelowest lift of the intake valves, and FIG. 9B shows a valve openingoperation under the lowest lift of the intake valves;

FIGS. 10A and 10B are views similar to FIGS. 9A and 9B, but in whichFIG. 10A shows a valve closing operation under the highest lift of theintake valves, and FIG. 10B shows a valve opening operation under thehighest lift of the intake valves;

FIG. 11 is a graph showing a valve lift characteristic of each intakevalve, which is provided by the variable valve system of the presentinvention;

FIG. 12 is a front perspective view of a guide cap used in the presentinvention;

FIG. 13 is a back perspective view of the guide cap; and

FIGS. 14 to 18 are views for explaining the steps for properlyconnecting a lever member of the actuating mechanism to the controlshaft.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the present invention will be described in detail withreference to the accompanying drawings.

For ease of understanding, various directional terms, such as, right,left, upper, lower, rightward and the like are used in the followingdescription. However, such terms are to be understood with respect toonly a drawing or drawings on which corresponding part or portion isshown.

Before describing the detail of the invention, an outlined constructionof a variable valve system 100 of the invention will be described withreference to FIGS. 8, 9A, 9B, 10A and 10B.

As will be understood from FIG. 8, variable valve system 100 shown inthe drawing is designed for multi-cylinder internal combustion enginesof a type that has two intake valves 2 and 2 for each cylinder.

That is, variable valve system 100 is constructed to control operationof paired intake valves 2 and 2 (viz., engine valves) for each cylinderof the engine. Intake valves 2 and 2 are slidably guided by a cylinderhead 1 (see FIG. 9A) through valve guides (not shown). Each intake valve2 has a valve spring 3 for being biased in a closing direction, and hasa valve lifter 16 mounted on a stem thereof.

As will be described in detail hereinafter, variable valve system 100generally comprises a valve lift mechanism 4 that induces an open/closecondition of intake valves 2 and 2, a valve lift degree varyingmechanism 5 that is incorporated with valve lift mechanism 4 to vary alift degree (or work angle) of intake valves 2 and 2 and an actuatingmechanism 6 that actuates the valve lift degree varying mechanism 5(more specifically, a control shaft 32 of this mechanism 5) inaccordance with an operation condition of the engine.

It is to be noted that the work angle of engine valve 2 is an eventcorresponding to a period or span in terms of crank angle, that elapsesfrom a time when the valve 2 is just opened to a time when the valve 2is just closed in each operation cycle of the engine.

As is seen from FIG. 8, valve lift mechanism 4 comprises a hollow driveshaft 13 that is rotatably held on an upper portion of cylinder head 1through bearings 14 (see FIG. 9A), a drive cam 15 for each cylinder,that is fixed, through a press-fitting or the like, to hollow driveshaft 13 to rotate therewith, two swing cams 17 and 17 for eachcylinder, that are integrally mounted on a cylindrical camshaft 20rotatably disposed on hollow drive shaft 13 and operatively contact withvalve lifters 16 and 16 of intake valves 2 and 2 to induce an open/closeoperation of intake valves 2 and 2 and a power transmitting mechanism“PTM” that is arranged between drive cam 15 and each of swing cams 17and 17 to transmit a torque of drive cam 15 to swing cams 17 and 17.Actually, due to an after-mentioned linkage construction of powertransmitting mechanism “PTM”, the rotary motion of drive cam 15 isconverted to a swing motion of swing cams 17 and 17.

Hollow drive shaft 13 extends along an axis of the engine. Although notshown in the drawings, hollow drive shaft 13 has one end to which atorque is applied from a crankshaft of the engine through a sprocketfixed to the end of drive shaft 13 and a timing chain that is put aroundthe sprocket and the crankshaft. That is, drive shaft 13 is driven orrotated by the crankshaft of the engine. Usually, an operation phasevarying mechanism (not shown) is arranged between the crankshaft anddrive shaft 13 for varying or controlling an operation phase of driveshaft 13 relative to the crankshaft of the engine.

As is seen from FIG. 9A, each of bearings 14 comprises a main bracket 14a that is mounted on cylinder head 1 to rotatably support drive shaft13, a sub-bracket 14 b that is mounted on main bracket 14 a to rotatablysupport an after-mentioned control shaft 32 and a pair of connectingbolts 14 c and 14 c that pass through both sub-bracket 14 b and mainbracket 14 a to tightly connect these brackets 14 b and 14 a to cylinderhead 1.

Drive cam 15 is a circular disc that has a center axis “Y” displaced oreccentric from a center axis “X” of drive shaft 13. More specifically,the circular disc 15 has at an eccentric portion thereof a circularopening through which drive shaft 13 passes. For the integral rotationof drive cam 15 with drive shaft 13, drive shaft 13 is secured to thecircular opening of the drive cam 15 through press-fitting or the like.

The two swing cams 17 and 17 are substantially the same in constructionand have a generally triangular cross section. These two swing cams 17and 17 are integrally mounted on axially opposed end portions ofcylindrical camshaft 20 that is swingably disposed about hollow driveshaft 13.

As shown in FIG. 9A, each swing cam 17 has a cam nose portion 21 and acam surface 22 at its lower side.

As is seen from this drawing, cam surface 22 of each swing cam 17includes a base round part that extends around the cylindrical outersurface of camshaft 20, a lump part that extends from the base roundpart toward cam nose portion 21 and a lift part that extends from thelump part to a maximum lift point defined at the leading end of cam noseportion 21. That is, under operation, these parts of cam surface 22slidably contact an upper surface of the corresponding valve lifter 16thereby to induce the open/close operation of the corresponding intakevalve 2 in accordance with a swing movement of swing arms 17 and 17.

As is understood from FIG. 8, power transmitting mechanism “PTM”comprises a rocker arm 23 that is pivotally disposed about control shaft32 positioned above drive shaft 13, a link arm 24 that pivotallyconnects one wing part 23 a (see FIG. 9A) of rocker arm 23 to drive cam15, and a link rod 25 that pivotally connects the other wing part 23 bof rocker arm 23 to one of swing cams 17 and 17.

As is seen from FIGS. 8 and 9A, rocker arm 23 has at its middle part acylindrical bore (no numeral) in which an after-mentioned control cam 33is rotatably disposed.

As shown in FIG. 9A, wing part 23 b of rocker arm 23 is pivotallyconnected to one end of link rod 25 through a pivot pin 27. The otherwing part 23 a of rocker arm 23 is pivotally connected to a radiallyprojected arm portion 24 b of link arm 24 through a pivot pin 26.

The two wing parts 23 a and 23 b of rocker arm 23 extend radiallyoutward from axially opposed end portions of the bored middle part ofrocker arm 23.

As is understood from FIG. 9A, link arm 24 comprises an annular baseportion 24 a that rotatably receives therein the above-mentioned drivecam 15 and the above-mentioned radially projected arm portion 24 b thatis pivotally connected to wing part 23 a of rocker arm 23 through pivotpin 26.

As is best seen from FIGS. 8 and 9A, link rod 25 is a curved channelmember that has an upper end 25 a pivotally connected to wing part 23 bof rocker arm 23 through pivot pin 27 and a lower end 25 b pivotallyconnected to swing cam 17 through a pivot pin 28.

Although not shown in the drawings, pivot pins 26, 27 and 28 areequipped at one ends with respective snap rings for holding link arm 24and link rod 25 at their properly set positions.

In the following, valve lift degree varying mechanism 5 will bedescribed in detail with reference to the drawings.

As is seen from FIG. 8, valve lift degree varying mechanism 5 comprisescontrol shaft 32 that extends in parallel with the above-mentioned driveshaft 13 and is rotatably held by bearings 14 (see FIG. 9A), and acontrol cam 33 for each cylinder, which is secured to control shaft 32to rotate therewith. As has been mentioned hereinabove, control cam 33is rotatably disposed in the cylindrical bore provided in the middlepart of rocker arm 23. That is, control cam 33 serves as a swingingfulcrum of rocker arm 23.

As is described hereinabove and seen from FIGS. 1, 2 and 9A, controlshaft 32 is rotatably held between main-bracket 14 a and sub-bracket 14b of each bearing 14 that is tightly mounted on cylinder head 1.

As is seen from FIGS. 1 and 3, control shaft 32 is integrally formed, atan end portion thereof near actuating mechanism 6, with a trapezoidalflange 32 a that has at radially projected two portions respectivethreaded bores 32 b. It is however to be noted that these bores 32 b arenot positioned at diametrically opposite portions of control shaft 32.That is, the bores 32 b are provided at asymmetric positions withrespect to an axis of control shaft 32.

As is best seen from FIG. 3, at a left end of control shaft 32, there isintegrally formed an annular projection 32 c that projects leftward froma center portion of the trapezoidal flange 32 a.

As is seen from FIGS. 1 and 2, for controlling or restricting a rotationrange of control shaft 32, there is provided a stopper mechanism 29.

Stopper mechanism 29 comprises first and second stopper pins 29 a and 29b that are projected from sub-bracket 14 b of bearing 14, and a stopperarm 29 c that is fixed to control shaft 32. As is seen from thesedrawings, upon rotation of control shaft 32, stopper arm 29 c is broughtinto contact with first or second stopper pin 29 a or 29 b thereby torestrict the rotation range of control shaft 32.

As is seen from FIG. 9A, control cam 33 is a circular disc that has acenter axis “P2” displaced or eccentric from a center axis “P1” ofcontrol shaft 32. More specifically, the circular disc 33 has at aneccentric portion thereof a circular opening through which control shaft32 passes. For the integral rotation of control cam 33 with controlshaft 32, control shaft 32 is secured to the circular opening of controlcam 33 through press-fitting or the like.

In the following, actuating mechanism 6 will be described with referenceto FIGS. 1 to 5 and 8. It is to be noted that actuating mechanism 6shown in FIG. 8 has some parts removed for clarifying the arrangement ofessential elements of the mechanism 6.

As is seen from FIG. 1, actuating mechanism 6 generally comprises acylindrical housing 35 that is mounted on one end of cylinder head 1 ina manner to extend perpendicular to control shaft 32 and thusperpendicular to drive shaft 13, an electric motor 36 that is connectedto one axial end of cylindrical housing 35, and a ball-screw typetransmission mechanism 37 that is installed in cylindrical housing 35for transmitting a torque of electric motor 36 to control shaft 36 whilereducing the rotation speed.

As is seen from FIGS. 4 and 5, cylindrical housing 35 is constructed ofan aluminum alloy or the like and includes generally an elongate lowerbore 35 a that extends axially along the housing 35 and an upper bore 35b that extends upward from a middle portion of elongate lower bore 35 a.That is, these two bores 35 a and 35 b are merged to constitute aso-called part housing room. As shown, in elongate lower bore 35 a,there is arranged the above-mentioned ball-screw type transmissionmechanism 37, and into upper bore 35 b, there is projected trapezoidalflange 32 a of control shaft 32.

Although not shown in FIG. 1, the two bores 35 a and 35 b haverespective openings that are covered by respective covers throughsealing members. As shown in FIG. 4, elongate lower bore 35 a has a leftend 35 c opened and a right end closed by a wall 35 d.

As is seen from FIGS. 4 and 8, electric motor 36 is of a DC type whichcomprises a cylindrical casing 38 that has an opened base end 38 atightly connected to the opened end 35 c (see FIG. 4) of elongate lowerbore 35 a. Electric motor 36 has an output shaft 36 a rotatably held bya retainer 39 tightly received in the opened left end 35 c (see FIG. 4).For sealing output shaft 36 a, there is provided a mechanical sealbetween retainer 39 and output shaft 36 a.

As is seen from FIG. 8, electric motor 36 is controlled by a controlunit 40. That is, control unit 40 outputs an instruction signal toelectric motor 36 by processing various information signals fed thereto.These information signals are, for example, signals from a crank anglesensor 41, an air flow meter 42, an engine cooling water temperaturesensor 43 and a rotation angle sensor 44 for control shaft 32. Byprocessing these information signals, control unit 40 derives a currentoperation condition of the engine and outputs an instruction signal toelectric motor 36 in accordance with the derived operation condition ofthe engine.

Referring back to FIG. 4, ball-screw type transmission mechanism 37generally comprises a ball-screw shaft 45 that extends axially inelongate lower bore 35 a to be coaxially connected to output shaft 36 aof electric motor 36, a ball-nut 46 that is disposed about ball-screwshaft 45 to operatively engage with the same, a lever member 47 that issecured to the above-mentioned trapezoidal flange 32 a of control shaft32 by means of connecting bolts 58, and a channel shaped link member 48that pivotally connects lever member 47 and ball-nut 46. Lever member 47and link member 48 thus constitute a transmission mechanism.

Ball-screw shaft 45 is formed with a threaded outer surface 49 exceptaxially opposite end portions 45 a and 45 b thereof. As shown in FIG. 4,opposite end portions 45 a and 45 b of ball-screw shaft 45 are rotatablyheld by left and right ball bearings 50 and 51 which are tightly held inelongate lower bore 35 a.

Left end portion 45 a of ball-screw shaft 45 has a hexagonal head 45 a′that is axially movably received in a hexagonal socket 52 that is fixedto a leading end of output shaft 36 a of electric motor 36. Thus, outputshaft 36 a and ball-screw shaft 45 can rotate together like a singleunit while being permitted to move axially relative to each other.

As is seen from FIGS. 4, 5 and 8, ball-nut 46 is meshed with ball-screwshaft 45 so that rotation of ball-screw shaft 45 about its axis inducesa forward or rearward movement of ball-nut 46 along ball-screw shaft 45.That is, ball-nut 46 is a cylindrical member that has a bore whose innersurface is formed with a spiral thread 53 that is meshed with a spiralthread 49 formed on the outer surface of ball-screw shaft 45.

A plurality of fine balls 54 are operatively received in spiral thread53 of ball-nut 46 for achieving a smoothed movement of ball-nut 46 alongball-screw shaft 45. Two deflectors (no numerals) are provided by spiralthread 53 of ball-nut 46 to produce an endless screw passage of thethreads in and along which fine balls 54 run endlessly under movement ofball-nut 46 along ball-screw shaft 45.

Thus, in operation, rotation of ball-screw shaft 45 about its axis isconverted to the axial movement of ball-nut 46 through fine balls 54.

As is seen from FIG. 4, ball-nut 46 is formed with a round projection 55to which lower ends of the above-mentioned link member 48 are pivotallyconnected through a pivot pin 57. As shown in FIG. 8, at axiallyopposite sides of round projection 55, there are provided curved cuts 56for permitting a swing movement of rounded lower ends of thechannel-shaped link member 48.

For achieving a proper positioning of ball-nut 46 at the time whentransmission mechanism 37 is being assembled in housing 35, there isprovided a position matching device.

That is, by using this position matching device, the leftmost positionof ball-nut 46 in FIG. 4 relative to ball-screw shaft 45 is assured. Inother words, the most-clockwise position of control shaft 32 in the samedrawing, that induces a minimum lift degree of intake valves 2, isassured.

That is, as is seen from FIGS. 3, 4 and 6, the position matching devicecomprises a threaded positioning opening 65 provided in a wall ofhousing 35 and an elongate positioning bolt 66 detachably fixed topositioning opening 65. As is seen from FIG. 4, positioning bolt 66 ispositioned just before left ball bearing 50.

As is seen from FIG. 6, when positioning bolt 66 is properly fixed topositioning opening 65, a rod portion 66 a of positioning bolt 66 servesas a stopper for stopping excessive axial movement of ball-nut 46. Thatis, in such case, left end surface 46 a of ball-nut 46 is brought intoabutment with rod portion 66 a of positioning bolt 66, as shown.

It is now to be noted that the position of ball-nut 46 determined bypositioning bolt 66 corresponds to an angular position of control shaft32 determined by the above-mentioned stopper mechanism 29 (see FIG. 1).That is, in such case, stopper arm 29 c of control shaft 32 is inabutment with first stopper pin 29 a, and as will be described in detailhereinafter, intake valves 2 of the engine are subjected to a minimumlift operation.

When the assembling work of transmission mechanism 37 is finished,positioning bolt 66 is removed and in place of it, a close bolt 67 isfitted to positioning opening 65, as is seen from FIG. 7.

As is seen from FIG. 4, between ball-nut 46 and right ball bearing 51,there is compressed through respective retainers 69 a and 69 b a coilspring 68 that is disposed about ball-screw shaft 45. Thus, coil spring68 functions to bias ball-nut 46 in such a direction as to induce theminimum lift operation of intake valves 2.

As is seen from FIG. 4, lever member 47 is trapezoidal in shape andcomprises a base portion 47 a that is secured to trapezoidal flange 32 aof control shaft 32 by means of two bolts 58 and a radially projectedportion 47 b that extends radially outward from base portion 47 a.

As is seen from FIG. 3, the two bolts 58 are engaged with theabove-mentioned asymmetrically arranged threaded bores 32 b of theflange 32 a of control shaft 32. For receiving bolts 58, base portion 47a of lever member 47 are formed with two arcuate openings 47 c. Althoughnot well shown in the drawings, each arcuate opening 47 c is shaped toextend around the axis of control shaft 32.

As is seen from FIGS. 1 and 3, lever member 47 is formed at its backsurface with an annular recess 47 d into which the above-mentionedannular projection 32 c of control shaft 32 is snugly received.

As is seen from FIG. 4, radially projected portion 47 b of lever member47 is formed with an opening (no numeral) through which anafter-mentioned pin 59 passes for pivotally connecting the link member48 to the radially projected portion 47 b.

Link member 48 having a generally U-shaped cross section is produced bypressing a flat metal plate. That is, link member 48 comprises twoparallel wall portions and a bridge portion that extends between the twoparallel wall portions.

As is seen from FIGS. 1 and 3, particularly FIG. 3, the above-mentionedrotation angle sensor 44 is arranged to face the lever member 47.

Rotation angle sensor 44 comprises a cylindrical metal member 60 that iscoaxially connected to the leading end of control shaft 32 passingthrough an opening 47 e of lever member 47. A round plastic holder 61 issecured to the leading end of cylindrical metal member 60. For thisfixing, an integral molding technique is used. As shown, round plasticholder 61 has the same diameter as the metal member 60. Round plasticholder 61 is formed with a diametrically extending groove (no numeral)in which a circular permanent magnet 62 is snugly and tightly received.As shown, the magnet 62 is received in the center part of the groove andthe depth of the groove is greater than the thickness of magnet 62.Although not shown in the drawings, the magnet 62 has at itsdiametrically opposed portions flat edges that intimately abut againstinner surfaces of the two walls that define therebetween the groove.With this, undesired radial leakage of magnetic force from the magnet 62is suppressed or at least minimized. It is to be noted that the magnet62 is positioned away from heads of bolts 58 by a sufficient distance.

As is best seen from FIG. 3, rotation angle sensor 44 further comprisesa plastic circular casing 63 that is fixed to the housing 35. For thisfixing, a stepped portion of circular casing 63 is snugly received in acircular opening 35 e of housing 35. Circular casing 63 is formed at aninner side thereof with a cylindrical recess 63 a that receives thereinround plastic holder 61 keeping an annular clearance therebetween. AHall-element 64 is embedded in circular casing 63 in a manner tosurround the round plastic holder 61.

As is seen from FIG. 8, information signal produced by rotation anglesensor 44 is processed by control unit 40. By detecting the N-pole andS-pole from the magnet 62, the rotation angle sensor 44 senses arotation angle (or angular position) of control shaft 32, that is fed tocontrol unit 40.

It is to be noted that, as is understood from FIGS. 3, 14 and 15, toopening 35 e of housing 35, there is detachably fitted a guide cap 70for keeping the connection between lever member 47 and link member 48 atthe time when various parts of the actuating mechanism 6 are beingassembled in housing 35.

The detailed construction of guide cap 70 is shown in FIGS. 12 and 13.Guide cap 70 is made of a molded plastic and comprises a cylindrical capproper 70 a that is to be fitted in the opening 35 e of housing 35, aflange portion 70 b that is integrally formed on one axial end of thecap proper 70 a, and a curved recess 70 c provided at a bottom portionof cap proper 70 a. For the purpose that will be described hereinafter,the curved recess 70 c has such a shape as to correspond to a unit thatincludes lever member 47 and link member 48.

Furthermore, guide cap 70 has a cylindrical recess 70 d into which theabove-mentioned round plastic holder 61 is to be inserted. As shown, thecylindrical recess 70 d is exposed to a generally middle portion of thecurved recess 70 c. Furthermore, guide cap 70 has at both sides ofcylindrical recess 70 d a pair of openings 70 e into which the heads ofthe above-mentioned bolts 58 are to be roughly inserted. These openings70 e are larger than heads of bolts 58. As shown, these paired openings70 e are exposed to longitudinally opposed portions of the curved recess70 d.

In the following, steps for connecting lever member 47 to control shaft32 and assembling rotation angle sensor 44 after assemblage of actuatingmechanism 6 to cylinder head 1 will be described in detail withreference to FIGS. 6 and 14 to 18.

As is seen from FIG. 14, prior to connecting housing 35 of actuatingmechanism 6 to cylinder head 1 by means of four connecting bolts 71, theabove-mentioned positioning bolt 66 is deeply engaged with positioningopening 65 of housing 35 and ball-screw shaft 45 is turned in adirection about its axis to cause ball-nut 46 to take the leftmostposition in FIG. 4 contacting with rod portion 66 a of positioning bolt66, as is understood from FIG. 6.

Then, guide cap 70 is fitted into opening 35 e of housing 35 assuring apositioning therebetween. As is seen from FIG. 15 that shows a back viewof housing 35, upon fitting of guide cap 70 into opening 35 e, a givenpart of guide cap 70 pushes ball-nut 46 to turn about the shaft 45 in adirection to near electric motor 36, so that the curved recess 70 c ofguide cap 70 neatly receive both lever member 47 and link member 48keeping the leftmost position of ball-nut 46 that is in contact with rodportion 66 a of positioning bolt 66.

Thus, lever member 47 and link member 48 are suppressed from making afree movement as well as inclination toward this side in FIG. 15. Then,with this condition kept, base portion 47 a of lever member 47 isbrought into contact with flange 32 a of control shaft 32 whileinserting the annular projection 32 c of control shaft 32 into annularrecess 47 d of base portion 47 a, as will be understood from FIG. 3.With this, coaxial arrangement between control shaft 32 and lever member47 is assured.

Then, as is seen from FIG. 16, after passing through openings 70 e ofguide cap 70 and arcuate openings 47 c of lever member 47, the two bolts58 are engaged with threaded bores 32 b of flange 32 a of control shaft32. During this time, by using the arcuate shape of the openings 47 c,base portion 47 a of lever member 47 is somewhat turned relative toflange 32 a of control shaft 32 to assure a proper positioning betweenlever member 47 and flange 32 a of control shaft 32. Then, the two bolts58 are strongly turned against threaded bores 32 b of flange 32 a. Withthis, lever member 47 is properly fixed to the flange 32 a of controlshaft 32, in such a manner as is shown in FIG. 3.

Then, as is seen from FIG. 17, guide cap 70 is detached from opening 35e of housing 35. Thus, under this condition, cylindrical metal member60, round plastic holder 61, permanent magnet 62 and heads of the bolts58 are exposed to the outside through the opening 35 e, as is seen fromthis drawing.

Then, as is seen from FIG. 18, plastic circular casing 63 is fitted tocircular opening 35 e of housing 35 and secured to the same by means oftwo bolts 72. Thereafter, positioning bolt 66 is removed frompositioning opening 65, and as is seen from FIG. 7, close bolt 67 isfixed to positioning opening 65 to close the same. Then, a terminal (notshown) provided on circular casing 63 is connected to control unit 40 bya suitable harness.

In the following, operation of variable valve system 100 actuated byactuating mechanism 6 will be briefly described with reference to thedrawings, particularly FIGS. 4, 5, 8, 9A, 9B, 10A and 10B.

For ease of understanding, the description on the operation will becommenced with respect to a condition wherein the associated enginestarts to run at a lower speed, such as a speed at idling.

In such case, as is seen from FIG. 5, electric motor 36 is actuated inaccordance with an instruction signal outputted from control unit 40. Asis seen from FIG. 4, upon this, a torque produced by electric motor 36is transmitted to ball-screw shaft 45 to rotate the same. With this,ball-nut 46 is moved axially leftward along ball-screw shaft 45 allowingfine balls 54 to run in and along a passage that is defined by andbetween spiral thread 53 of ball-nut 46 and spiral thread 49 ofball-screw shaft 45. That is, ball-nut 46 is moved toward electric motor36 and finally to the leftmost position that has been determined bypositioning bolt 66.

During the leftward movement of ball-nut 46 on ball-screw shaft 45,lever member 47 and thus control shaft 32 are turned clockwise in FIG.4. (It is to be noted that the clockwise turning of control shaft 32 inFIG. 4 induces a counterclockwise turning of the same in FIGS. 9A to10B).

Upon this, as is seen from FIGS. 9A and 9B, control cam 33 secured tocontrol shaft 32 is turned counterclockwise about the axis “P1” ofcontrol shaft 32 moving the thickest cam part thereof upward away fromdrive shaft 13, and finally control cam 33 takes the angular position asshown in these drawings. In other words, in this case, the entireconstruction of rocker arm 23 takes a relatively high position. Thus,under this condition, as is seen from FIG. 9A, the uppermost positionthat can be taken by pivot pin 27 provided between left wing part 23 bof rocker arm 23 and upper end 25 a of link rod 25 is a first positionthat is remote from drive shaft 13. This means that as is seen fromFIGS. 9A and 9B, under operation of the variable valve system 100, linkrod 25 and thus swing cam 17 are forced to operate at a position remotefrom valve lifter 16.

Accordingly, when, due to rotation of drive shaft 13, drive cam 15 isrotated in annular base portion 24 a of link arm 24, rocker arm 23 isforced to swing reciprocating link rod 25 and swing cam 17 at such aposition remote from valve lifter 16. That is, as is understood fromFIG. 9B and the graph of FIG. 11, under this condition, the valve liftshows the smallest degree “L1” inducing a retarded open timing of intakevalves 2 and 2 thereby minimizing the over wrap period with theassociated exhaust valves. Thus, improved fuel consumption and stablerunning of the engine are obtained under such lower speed condition ofthe engine. In FIG. 11, reference “BDC” indicates a bottom dead centerand reference “TDC” indicates a top dead center.

While, when the engine is subjected to a high speed operation, controlunit 40 (see FIG. 8) controls electric motor 36 to run in a reverseddirection. As is seen from FIG. 5, upon this, ball-nut 46 is movedrightward on and along ball-screw shaft 45. That is, ball-nut 46 ismoved away from electric motor 36 allowing fine balls 54 to run in andalong the passage defined by and between spiral thread 53 of ball-nut 46and spiral thread 49 of ball-screw shaft 45.

Accordingly, as is seen from FIG. 5, lever member 47 and thus controlshaft 32 are turned counterclockwise in the drawing. (It is to be notedthat the counterclockwise turning of control shaft 32 in FIG. 5 inducesa clockwise turning of the same in FIGS. 9A to 10B).

Upon this, as is seen from FIGS. 9A, 10A and 10B, control cam 33 isturned clockwise about the axis “P1” of control shaft 32 moving thethickest cam part thereof downward toward drive shaft 13, and finallycontrol cam 33 takes the angular position as shown in FIGS. 10A and 10B.In other words, in this case, the entire construction of rocker arm 23takes a relatively low position. Thus, under this condition, as is seenfrom FIG. 10A, the uppermost position that can be taken by pivot pin 27is a second position that is near drive shaft 13 as compared with theabove-mentioned first position. This means that as is seen from FIGS.10A and 10B, under operation of variable valve system 100, link rod 25and thus swing cam 17 are forced to operate at a position near valvelifter 16.

Accordingly, when, due to rotation of drive shaft 13, drive cam 15 isrotated in annular base portion 24 a of link arm 24, rocker arm 23 isforced to swing reciprocating link rod 25 and swing cam 17 at such aposition near valve lifter 16. That is, as is seen from FIG. 10B and thegraph of FIG. 11, under this condition, the valve lift shows the largestdegree “L2”. As is seen from the graph of FIG. 11, the close timing ofeach intake valve 2 is retarded in accordance with an advancement of theopen timing. That is, the work angle is increased. Thus, intake aircharging efficiency is increased and thus sufficient engine power isobtained in such high speed condition.

As is described hereinabove, in accordance with the present invention,due to employment of the position matching device (65, 66) that includesthreaded positioning opening 65 of housing 35 and positioning bolt 66detachably connectable to the opening 65, the most-moved position (viz.,the leftmost position in FIG. 4) of ball-nut 46 can be previously set,which matches with the most-tuned angular position of control shaft 32determined by the stopper mechanism 29. Accordingly, even afterpositioning bolt 66 is removed from the opening 65, the most-movedposition of ball-nut 46 is assuredly provided by the stopper mechanism29. This means that as is understood from FIG. 4 under such most-movedpositioning of ball-nut 46, there is left a certain clearance betweenball bearing 50 and ball-nut 46 and thus the most-turned angularposition of control shaft 32 is not affected by the operation range ofball-nut 46.

That is, as is seen from FIG. 1, under the most-turned angular positionof control shaft 32 wherein stopper arm 29 c contacts first stopper pin29 a, intake valves 2 are forced to show their smallest lift degree “L1”as is shown by FIGS. 9A and 9B. In this case, as is seen from FIG. 4,ball-nut 46 stays near ball bearing 50 without contacting the same.Thus, the angular operation range of control shaft 32 is not affected bythe most-moved position of ball-nut 46, but affected by only the stoppermechanism 29.

Accordingly, control shaft 32 can have a higher positioning accuracy atthe most-turned angular position, which brings about a higher valve liftcontrollability of intake valves 2.

As is mentioned hereinabove, due to practical usage of guide cap 70,lever member 47 and link member 48 can be stably held keeping therelative positioning therebetween at the time of assembling theactuating mechanism 6. Thus, the work for connecting the lever member 47to control shaft 32 is readily and precisely carried out. Furthermore,the practical usage of guide cap 70 facilitates the convey of actuatingmechanism 6 to a desired position, and facilitates the preparation forconnecting the actuating mechanism 6 to an associated engine.

After connecting the lever member 47 to control shaft 32, guide cap 70is removed from opening 35 e of housing 35 and plastic circular casing63 is fitted to opening 35 e to close the same. Casing 63 thus has afunction to close opening 34 e as well as a function to holdHall-element 64, which means reduction in number of parts used and thusreduction in cost.

Furthermore, due to usage of guide cap 70, the work for turning bolts 58to fix lever member 47 to flange 32 a of control shaft 32 is readilymade. Actually, openings 70 e of guide cap 70 that accommodate heads ofbolts 58 serve as a guide means for bolts 58. Presence of openings 70 efacilitates the work for detaching guide cap 70 from opening 35 e ofhousing 35.

Due to usage of close bolt 67 fitted to positioning opening 65, theinterior of housing 35 is protected from dust and the like.

Due to usage of coil spring 68 that biases ball-nut 46 in an axialdirection, backlash of ball-nut 46 is suppressed or at least minimized.Furthermore, due to presence of such coil spring 68, direct contact ofball-nut 46 against the other ball bearing 51 is avoided.

For example, the arrangement of electric motor 32 may change inaccordance with the layout of engine room. Furthermore, in place ofelectric motor 32, a hydraulic motor or the like may be used.

For connecting round plastic holder 61 to the leading end of cylindricalmetal member 60 (see FIG. 1), a threaded coupling or the like may beused. The diameter of the holder 61 may change in accordance with sizeof permanent magnet 62. The holder 61 may be made of a hard rubber,aluminum or the like as long as it exhibits a non-magneticcharacteristic.

In place of ball-screw shaft 45 and ball-nut 46 that employ a pluralityof fine balls 54, a normal bolt-nut arrangement may be used.

Although the foregoing description is directed to the system forcontrolling intake valves 2 of the engine, the present invention isapplicable to exhaust valves and both intake and exhaust valves.

The entire contents of Japanese Patent Application 2004-177783 filedJun. 16, 2004 are incorporated herein by reference.

Although the invention has been described above with reference to theembodiment of the invention, the invention is not limited to suchembodiment as described above. Various modifications and variations ofsuch embodiment may be carried out by those skilled in the art, in lightof the above description.

1. A variable valve system of an internal combustion engine for varyingan operation manner of an engine valve by controlling an angularposition of a control shaft, comprising: a stopper mechanism thatdetermines an angular range in which the control shaft is permitted torotate about its axis; an actuating mechanism that actuates the controlshaft to rotate about its axis; and a position matching device separatefrom the stopper mechanism that is practically assembled only when theactuating mechanism is being assembled, the position matching devicewhen assembled restricting operation of the actuating mechanism in sucha manner as to match a maximally operated position of the actuatingmechanism with a maximally operated angular position of the controlshaft.
 2. A variable valve system as claimed in claim 1, in which theactuating mechanism comprises: an externally threaded shaft that isturned about its axis in accordance with the operation condition of theengine; an internally threaded nut member operatively engaged with thethreaded shaft so that turning of the threaded shaft induces an axialmovement of the nut member along the threaded shaft, the nut memberbeing contactable with the position matching device when the latter isassembled; a lever member connected to the control shaft to rotatetherewith; a link member that pivotally connects the lever member andthe nut member; and a guide member that is detachably connected to ahousing of the actuating mechanism, the guide member, when connected tothe housing, holding both the lever member and the link member keeping agiven clearance between the nut member and a stopper means in thehousing, the guide member being removed from the housing once theconnection between the lever member and the link member is properlyachieved.
 3. A variable valve system as claimed in claim 2, furthercomprising: a first member connected to the lever member to rotatetherewith; and a second member connected to the housing and arranged tosurround the first member, wherein the first member and second memberconstitute a rotation angle sensor that detects the angular portion ofthe control shaft.
 4. A variable valve system as claimed in claim 3, inwhich an end of the control shaft is formed with a flange portion thatis formed with threaded openings, in which the lever member is formedwith bolt openings through which connecting bolts pass before beingengaged with the threaded openings of the flange portion thereby tosecure the lever member to the flange portion and in which the guidemember is formed with openings that have a size larger than heads of theconnecting bolts.
 5. A variable valve system as claimed in claim 2, inwhich the guide member is formed with a curved recess that is shaped tosnugly receive therein a unit that includes the lever member and thelink member.
 6. A variable valve system as claimed in claim 2, in whichthe lever member is formed with bolt openings through which bolts passbefore being engaged with threaded openings formed in a flange portionformed on an end of the control shaft, the lever member and the flangeportion having at their mutually facing portions male-femaleconstructions that are mated when the lever member and the flangeportion are secured to each other, and in which the bolts openings ofthe lever member are elongate openings that extend around the axis ofthe control shaft.
 7. A variable valve system as claimed in claim 1, inwhich the actuating mechanism comprises: an externally threaded shaftthat is turned about its axis in accordance with the operation conditionof the engine; an internally threaded nut member operatively engagedwith the threaded shaft so that turning of the threaded shaft induces anaxial movement of the nut member along the threaded shaft, the nutmember being contactable with the position matching device when thelatter is assembled; a lever member connected to the control shaft torotate therewith; a link member that pivotally connects the lever memberand the nut member; and a housing that houses therein the threadedshaft, the threaded nut member, the lever member and the link member,and in which the position matching device comprises a positioningopening formed in the housing at a position where the nut member arriveswhen the same is maximally moved along the threaded shaft, thepositioning opening being adapted to hold a positioning bolt that isprojected into the housing to stop an excessive movement of the nutmember.
 8. A variable valve system as claimed in claim 7, furthercomprising a close bolt that is connected to the positioning opening inplace of the positioning bolt once assemblage of the actuating mechanismis substantially finished.
 9. A variable valve system as claimed inclaim 1, further comprising: a drive shaft synchronously rotated aboutits axis by a crankshaft of the engine, the drive shaft having a drivecam connected thereto; a swing cam rotatably supported by the driveshaft, the swing cam having a cam surface that is contactable with avalve lifter of the engine valve to induce an open/close movement of theengine valve; and a rocker arm having one end operatively connected tothe drive cam through a link arm and the other end operatively connectedto the swing cam through a link rod, wherein when, upon energization ofthe actuating mechanism, the control shaft is rotated about its axis toassume a new angular position, a swing fulcrum of the rocker arm ischanged and thus a position where the cam surface of the swing camcontacts the valve lifter is changed thereby varying the lift degree ofthe engine valve.
 10. A variable valve system as claimed in claim 7, inwhich the positioning opening is internally threaded and in which anexternally threaded portion of the positioning bolt is engaged with thethreaded positioning opening.
 11. A variable valve system as claimed inclaim 7, in which the positioning opening is internally threaded and inwhich an externally threaded portion of a close bolt is engaged with thethreaded positioning opening once the assemblage of the actuatingmechanism is substantially finished.
 12. A variable valve system asclaimed in claim 7, in which the positioning bolt is temporallyconnected to the positioning opening.
 13. A variable valve system asclaimed in claim 7, further comprising a biasing member that is providedbetween the nut member and the housing to bias the nut member in a givenaxial direction of the threaded shaft.
 14. A variable valve system of aninternal combustion engine for varying an operation manner of an enginevalve by controlling an angular position of a control shaft, comprising:a stopper mechanism that determines an angular range in which thecontrol shaft is permitted to rotate about its axis; and an actuatingmechanism that actuates the control shaft to rotate about its axis, theactuating mechanism comprising: an externally threaded shaft that isturned about its axis in accordance with the operation condition of theengine; an internally threaded nut member operatively engaged with thethreaded shaft so that turning of the threaded shaft induces an axialmovement of the nut member along the threaded shaft, the nut memberbeing contactable with the position matching device when the latter isassembled; a transmission mechanism provided between the control shaftand the nut member to convert the axial movement of the nut member to arotary motion of the control shaft; a housing that houses therein thethreaded shaft, the threaded nut member and the transmission mechanism;and a position matching device that is practically assembled only whenthe actuating mechanism is being assembled, the position matching devicewhen assembled restricting operation of the actuating mechanism in sucha manner as to match a maximally operated position of the actuatingmechanism with a maximally operated angular position of the controlshaft.
 15. A variable valve system as claimed in claim 14, in which thetransmission mechanism comprises a lever member connected to the controlshaft to rotate therewith; and a link member that pivotally connects thelever member and the nut member, and further comprises a guide memberthat is detachably connected to the housing of the actuating mechanism,the guide member, when connected to the housing, holding both the levermember and the link member keeping a given clearance between the nutmember and a stopper means provided in the housing, the guide memberbeing removed from the housing once the connection between the levermember and the link member is properly achieved.
 16. A variable valvesystem as claimed in claim 15, further comprising: a drive shaftsynchronously rotated about its axis by a crankshaft of the engine, thedrive shaft having a drive cam connected thereto; a swing cam rotatablysupported by the drive shaft, the swing cam having a cam surface that iscontactable with a valve lifter of the engine valve to induce anopen/close movement of the engine valve; and a rocker arm having one endoperatively connected to the drive cam through a link arm and the otherend operatively connected to the swing cam through a link rod, whereinwhen, upon energization of the actuating mechanism, the control shaft isrotated about its axis to assume a new angular position, a swing fulcrumof the rocker arm is changed and thus a position where the cam surfaceof the swing cam contacts the valve lifter is changed thereby varyingthe lift degree of the engine valve.
 17. A variable valve system asclaimed in claim 14, in which the position matching device comprises: apositioning opening formed in the housing at a position where the nutmember arrives when the same is maximally moved along the threadedshaft; and a positioning bolt that is engageable with the positioningopening to be projected into the housing to stop an excessive movementof the nut member.
 18. A variable valve system as claimed in claim 17,further comprises a close bolt that is connected to the positioningopening in place of the positioning bolt once assemblage of theactuating mechanism is substantially finished.